The present invention relates to electrically actuatable light filters for temporally modulating incident light to produce colored images dependent upon the applied controlling electrical signals. The invention is based on the Fabry-Perot interferometer conceived in 1899. This interferometric concept utilizes the optical interference effects generated between two mirrored surfaces positioned in planar proximity to one another at distances of the order of the wavelength of light. Both constructive and destructive interference conditions can be created resulting in transmission or reflection of incident light. In the intervening time period since inception, many interferometer designs have been forthcoming and in latter years piezoelectrically controlled mirror motion has allowed many new applications. Most recently, with the advent of silicon micromachining technology, an interferometer comprising a single crystal silicon substrate and electrostatic actuation has been patented by S. R. Mallinson; U.S. Pat. No. 4,825,262 entitled "Fabry-Perot Interferometer".
Color filters find widespread application in the camera industry where the most common technology employed for color video cameras is the well known vidicon tube. This well-developed scanning electron beam and light sensitive conductor technology has the disadvantage, however, of requiring three tubes for a color system and of being relatively expensive to manufacture.
A second color camera technology gaining importance, especially in smaller camera applications, is the solid state image sensor. This sensor technology requires low driving voltages and operates with a three element color filter array to produce a three-color signal. A flat planar construction makes it attractive for small physical volume applications. It has an acceptable color capability but similarly requires three sensor elements per color cell or pixel. An example of such color camera technology is represented in U.S. Pat. No. 3,971,065 entitled, "Color Imaging Array", to B. E. Bayer.
Although the production of color and color images in the photographic, display and video fields has been almost exclusively the technique of high resolution spatial combination of three-color primaries, the high speed temporal or time based addition of color primaries to produce color sensation has been recognized for many years. In fact, as early as 1926, J. Guild had published ("A Trichromatic Colorimeter Suitable for Standardization Work", Transactions Optical Society, 1926, vol. 27, page 106) the constructional details of a high-speed rotating three-color filter based colorimeter. For the human observer exposed to a rapidly changing temporal color stimulus, the visual sensation arises from a biological visual integration process occurring during the time interval of the persistence of vision. The resultantly observed color is thereby determined by the relative temporal amounts of the three primary components of the stimulus. Biologically, the three-component theory of color sensation has been attributed to the spectral sensitivities of the rod and cone structure of the human eye. The temporally based production of color constitutes an approach which is an alternative to the more widespread spatially based techniques.